Mertler etal.
thermal probe and pilot burner



March 1967 C.$.MERTLER ETAL 3,311,157

THERMAL PROBE AND PILOT BURNER 2 Sheets-Sheet 1 Filed July 9, 1964 p w EE M M W M m m 0 3 N? r 4 W in r fi mi ,0 a 7 4 M/ x M m M344 5 March 28,1967 c, 5, ER ETAL 3,311,157

THERMAL PROBE AND PILOT BURNER 2 Sheets-Sheet 2 Filed July 9, 1964 s m;w m; W W i 2% 5 w A W;

United States Patent 3,311,157 THERMAL PROBE AND PILOT BURNER Charles S.Mertler and Truman H. Cline, both of Mansfield, Ohio, assignors toStevens Manufacturing Company, Inc., a corporation of Ohio Filed July 9,1964, Ser. No. 381,419 4 Claims. (Cl. 158-125) This invention relates toa burner ignition unit for gas appliances.

Commonly, in various gas appliances, such as in the oven of a range, amain burner is arranged to be lighted by a pilot burner which isprovided with a flarme switch whose purpose is to detect whether thepilot burner is on or off. This flame switch controls a valve in the gassupply line to the main burner, so that the gas supply to the mainburner will be cut off if the pilot burner is off. The flame switch hasa thermal probe which, when heated by the pilot burner, expands tooperate the switch. For proper operation, the thermal probe must beproperly positioned with respect to the pilot burner flame, so that itwill operate in accordance with the performance characteristics forwhich it has been calibrated. For example, if the pilot flame is notclose enough to the thermal probe or is not properly directed withrespect to the thermal probe, the -probe will not heat fast enough norproperly to operate the switch in the manner intended.

Prior to the present invention, conventional arrangements of this typehave had separate mountings for the pilot burner and the associatedthermal probe. This required the gas appliance manufacturer to carefullymount the pilot burner both with respect to the main burner and withrespect to the thermal probe of the flame switch. In addition, separatemounting brackets were required for the pilot burner and the flameswitch, adding to the cost and physical size of the pilot burner andflame switch installation.

Where automatic electric ignition of the pilot burner was provided for,the prior arrangements commonly did not provide for operation of thepilot burner ignition coil, the flame switch, and theelectrically-operated main burner valve controlled by the flame switchfrom a single low voltage source.

The present invention is directed to a novel pilot burner and flameswitch unit which avoids these and other disadvantages inherent in priorarrangements for the same general purpose.

In accordance with the present invention the pilot burner and the flameswitch, including the thermal probe, are constructed as a rigid, compactunit whose component parts are accurately positioned with respect to oneanother to provide the calibrated performance characteristics, and onlya single mounting is required for the entire unit. The gas appliancemanufacturer is required only to mount the unit so as to position thepilot burner properly with respect to the main burner in the appliance.

The proper positioning of the pilot burner with respect to the thermalprobe is assured by the unitary, rigid construction of the pilot burnerand flame switch unit.

Preferably, also, the present ignition unit includes an electricignition coil firmly supported in igniting relationship to the pilotburner and electrically connected to the flame switch to light the pilotburner automatically when the usual pilot burner ignition control isoperated by the user of the appliance. Both the ignition coil and theflame switch may be connected to a single low voltage source ofelectricity, as is the electrically-operated main burner valve which iscontrolled by the flame switch, thereby simplifying the electrical powersupply requirements for the ignition system embodying the presentignition unit.

It is a principal object of this invention to provide a novel andimproved burner ignition unit for gas appliances.

Another object of this invention is to provide such an ignition unitwhich is compact, readily mounted, and requires no calibrationadjustment when being installed in the appliance.

Another object of this invention is to provide such an ignition unit inwhich the pilotburner and the flame switch are embodied in a unitarystructure which insures proper positioning of the pilot burner and thethermal probe of the flame switch with respect to one another.

Another object of this invention is to provide a novel and improvedelectric ignition unit which simplifies the power supply connections forthe complete ignition system in which it is embodied.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims, taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a top plan view of the presently-preferred embodiment of thepilot burner and flame switch unit according to the present invention;

FIGURE 2 is a longitudinal view, partly in elevation and partly insection, of the FIGURE 1 unit;

FIGURE 3 is an end elevational view of the unit, taken from the left endof FIGURE 2;

FIGURE 4 is an enlarged cross-section taken along the line 4-4 in FIGURE2;

FIGURE 5 is a fragmentary longitudinal section taken along the line 55in FIGURE 4 on a more enlarged scale;

FIGURE 6 is an enlarged fragmentary perspective view of the switch inthe present unit; and,

FIGURE 7 is a simplified schematic diagram of a burner ignition circuitin which the present pilot burner and flame switch unit is embodied.

Referring first to FIGURES 1 and 2, the ignition unit of the presentinvention comprises a rigid housing 10, an elongated pilot burner tube11 fixedly mounted on the housing and projecting therefrom andpresenting flame ports 12 in spaced relation to the housing, anelongated thermal probe 13 supported by housing 10 and projectingtherefrom generally parallel to the pilot burner tube to be heated bythe pilot flame at the latters flame ports 12, and a single pole, doublethrow switch 14 (FIGURE 2) positioned inside housing .10 to be operatedby thermal probe 13. A glow coil or ignition coil 15 is rigidlysupported from housing 10 in a position to light the pilot burner. Thisglow coil is electrically connected to switch 14 so that the glow coilmay be energized first to light the pilot burner, after which thethermal probe becomes heated by the pilot burner and operates the switchto deenergize the glow coil.

The switch housing 10 comprises a rigid metal front plate 16, aheat-resistant insulating body 17 such as a ceramic body, and a thinlayer 18 of insulation (such as mica) sandwiched between them. A pair ofscrews 19 (FIGURE 3) hold the housing parts assembled together. Theceramic body 17 is formed with a recess 20 of approximately rectangularoutline, as shown in FIGURE 4,

in which the switch 14 is located. An opening 21 (FIG- URE 2) extendsthrough the front plate 16 and the insulation layer 18 into this recess.This opening loosely receives the inner end of the thermal probe 13.

The front plate 16 of the housing has a depending portion 16a whichprojects below the bottom edge of the housing body 17, as shown inFIGURES 2 and 3. The pilot burner tube 11 extends through this portionof plate 16 and is welded at 22 to the front face of the latter. Fromthis location, the pilot burner tube 11 extends away tend perpendicularto one another.

from the front of the switch housing horizontally and then upward at anacute angle and then horizontally perpendicularly away from the housing.At the lastmentioned horizontal portion away from the switch housing,the pilot burner tube presents the longitudinally spaced, upwardlydirected flame ports 12 and presents at its underside an ignition port23. The right end or outboard end of the pilot burner tube 11 is closedby a rigid metal end plate or support member 24. The outboard end oftube 11 carries the thermal probe 13, and this is convenientlyaccomplished by carrying it in the end plate 24, which in turn isfastened to the outer end of the burner tube 11, as by welding at 25.

At the back side of the front plate 16 the pilot burner 11 extendshorizontally in back of the switch housing and is rigidly attached to anexternally screw threaded, annular inlet fitting 26. In use, fitting 26is connected to a gas line, which supplies fuel that flows through thepilot burner tube 11 and issues from the latter at the ignition port '23and the flame ports 12. The gas line may also support the entireassembly.

The pilot burner tube 11 is made of a suitable metal, such as astainless steel, which preferably has a low thermal coeificient ofexpansion.

The thermal probe 13 is an elongated tubular push rod of a suitablemetal, such as another type of stainless steel,

, which has a substantially different thermal coeflicient of expansionfrom that of the pilot burner, preferably a higher rate. As alreadymentioned, the left end of push rod 13 is loosely received in theopening 21 leading into the recess 20 in the housing body 17. This endof the push rod 13 is crimped over a rigid switch-operating pin 27 ofceramic or other suitable electrical insulation material, which projectsinto the recess 20 in the switch housing. The opposite (right) end ofpush rod 13 is slidably received in a hollow adjusting screw 28, whichis threadedly mounted in the end plate 24. A ball 29 is engaged betweenthis end of push rod 13 and the inner end of the conical recess 60 inthe adjusting screw. The ball 29 seating against the conical recess 60permits a degree of freedom of the end of push rod 13 in the adjustingscrew 28 for self-aligning purposes. Alternatively, the push rod 13 maybe fixed to the adjusting screw 28, if desired.

The switch 14 in the switch housing recess 20 comprises an electricallyconductive carrier or leaf spring 30 (FIG- URE 6) having a flat mountingportion 31, which is seated against the bottom wall 32 of the recess byan electrically. conductive rivet 33, as shown in FIGURE 5. Rivet 33extends through the back wall of the housing body 17 and at the backface of the latter it is attached to a rigid first terminal 33a (FIGURE3). The leaf spring 30"presentsan elongated, flexible and resilient,normally flat leaf 34, which is attached to the mounting portion-31 byan integral U-shaped portion 35, which provides a cantilever support forleaf 34. The switchoperating pin 27 extends perpendicular to leaf 34 andis positioned to engage the latter a short distance away from theU-shaped portion 35, as shown in FIGURE 6. The leaf 34 has an opening34' close to where it is engaged by the operating pin 27 for the purposeof access to the rivet 33. At its opposite free end the leaf 34 carriesmovable contact means in the form of first and secnd wire movablecontact members 36 and 37 on its opposite faces. The leaf spring 30constitutes a movable, electrically conductive carrier for the movablecontacts 36 and 37.

The first movable contact member 36 is positioned in confrontingrelationship to a first fixed wire contact member 38, which is attachedto a rigid, stationary, electrically conductive switch arm 39 carried byan electrically conductive rivet 40. The switch contact members 36 and38 ex- Rivet 40 extends through a spacer 40c and through the back wallof the I housing body 17 and at the back face of the latter it is"connected to'a rigid second terminal 40a (FIGURE 3),

which projects down beyond the switch housing. As shown in FIGURE 2,terminal 46a presents a rigid, forwardly extending, horizontal leg 40bat one side of the pilot burner tube 11.

The second movable contact member 37 carried by leaf 34 is positioned inconfronting relationship to a second fixed wire contact member 41, whichis attached to an electrically conductive rivet 42. Switch contactmembers 37 and 41 extend perpendicular to one another. Rivet 42 extendsthrough the back wall of the housing body 17 and at the latters backface it is connected to a third terminal 42a, which projects to one sideof the switch housing, as shown in FIGURE 3.

The leaf spring 30 has an inherent bias such that cantilever leaf 34normally positions the first movable contact 36 to engage the firstfixed contact 38 and positions the second movable contact 37 out ofengagement with the second fixed contact 41. When the operating pin 27moves to the left in FIGURES 2, 5 and 6, it displaces the leaf 34against the spring bias to move the first movable contact 36 out ofengagement with the first fixed contact 38 and to move the secondmovable contact 37 into engagement with the second fixed contact 41.

A rivet 43 mounts a fourth terminal 43a on the back of the housing body17. This terminal has a forwardly projecting rigid leg 43b (FIGURES land 3) which extends at the opposite side of the pilot burner tube 11from the terminal leg 40b.

The ignition coil 15 is electrically fastened at its opposite ends tothe free ends of the terminal legs 40b and 43b. With this arrangement,the ignition coil is supported by the terminal legs 40b and 43b in closeproximity to the ignition port 23 of the pilot burner tube 11 and isconnected electrically between the second and fourth terminals 40a and43a.

A shield plate 44 is fastened, as by welding, to the burner tube 11 andprojects rearwardly horizontally below the terminal legs 40b and 43b andthe glow coil 15 to protect these parts. This shield helps to preventdrafts from striking the pilot flame which might blow it out. Also alanced tongue 62 in the shield 44 carries an insulating tube 63 whichsupports the center of the ignition coil 15 against sagging.

With this construction of the pilot burner and flame switch unit, thepilot burner 11 and the thermal probe 13 are properly positioned withrespect to one another by virtue of the rigid mounting of the pilotburner on the switch housing 10 and the sliding fit of the thermal probein the same switch housing. There is no possibility that they may becomemisaligned by careless or rough handling by the personnel installingthem on the gas appliance. Only a single mounting bracket is requiredfor the complete unit, and when installing the unit the only matter ofconcern to the installer is to position the pilot burner properly withrespect to the main burner of the appliance. This enables a more exactmounting of the pilot burner with respect to the main burner; Also, thepresent ignition unit, due to its unitary construction, is extremelycompact and may much more readily be used with small sized main burnersand in compact heaters. The ignition coil, pilot burner and flame switchof the present ignition unit are all properly positioned with respect toeach other by the novel unitary, rigid construction describedhereinbefore.

The flame switch can be readily calibrated simply by adjusting the screw28, whose position determines the position of the thermal probe 13 andthe switch operating pin 27 at normal ambient temperatures.

When the pilot burner 11 is lighted, its flame at ports 12 heats thethermal probe 13. Both the pilot burner and the thermal probe areheated, but the probe 13 expands at a much faster rate when heated.Since the right end of the thermal probe 13 is supported by the endplate 24, the thermal probe will move to the left relative to the pilotburner tube 11 and the operating pin 27 carried by the thermal probewill displace the switch leaf 34 against its spring bias to open thenormally-closed first contacts 36, 28 and to close the normally-opensecond contacts 37, 41.

An alternative arrangement is to have the burner tube 11 and probe 13 ofthe same material. This provides complete ambient temperaturecompensation. Since the probe 13 is in the pilot flame and the burnertube 11 is not, there is a temperature differential between these twoparts, and hence a differential expansion to actuate the switch. Ineither case the thermal expansion of the probe 13 is greater because ofthe higher temperature of this probe.

FIGURE 7 shows the foregoing ignition unit schematically in an ovenburner ignition circuit.

The first terminal 330 of the present ignition unit is connected to thelower end of a secondary winding 45 of a step-down transformer 46, whoseprimary winding 47 is connected through a switch 48 across aconventional 110120 volt A.C. house current source 49. In one practicalembodiment, the secondary voltage of the transformer is 12 volts.

The upper end' of the transformer secondary winding 45 is connectedthrough a clock switch 50, an oven thermostat switch 51 and a conductor59 to the fourth terminal 43a of the present ignition unit.

Also, conductor 59 is connected to the third terminal 42a of the presentignition unit through an operating coil 52 for a valve 53 connected inthe gas supply line to a main burner 54 (either the bake burner or thebroil burner) in the oven. A manually operable main shutoff valve 55 isconnected between the gas inlet manifold 56 and theelectrically-operated main burner valve 53.

The switch 48 is under the control of a manually operable control knob57. The control knob also is arranged to operate a pilot burner valve 58connected to control the flow of gas from the outlet side of the mainshutofr" valve 55 to the pilot burner 11.

Initially, with the pilot burner unlit, the temperature of the thermalprobe 13 will be such that the first switch contacts 36 and 38 will beclosed and the second switch contacts 37 and 41 will be open, as shownin FIGURES 5 and 7.

Assuming that the clock switch and the oven therlowing takes place:

Gas is supplied to the pilot burner 11 and escapes from the ignitionport 23 and the flame ports 12 of the latter.

The ignition coil 15 is energized from the transformer 46 by way of thefirst terminal 33a, the first switch contacts 36 and 38, the secondterminal 40a, through the ignition coil 15 and thence to fourth switchterminal 43a. The ignition coil ignites the gas at the ignition port 23and the resulting flame at the pilot burner flame ports 12 heats thethermal probe 13.

Due to their different rates of heat expansion, the thermal probe 13expands lengthwise with respect to the pilot burner tube 11, andconsequently, the thermal probe moves to the left in FIGURE 2, forcingthe switch-operating pin 27 inward against the spring leaf 34 to openthe normally-closed first switch contacts 36 and 38 and to close thenormally-open second switch contacts 37 and 41.

The opening of the first switch contacts 36 and 38 disconnects theenergization circuit for the ignition coil 15.

The closing of the second switch contacts 37 and 41 completes anenergization circuit for the valve-operating coil 52 from transformer 46by way of the first switch terminal 33a, the second switch contacts 37,41 and the third terminal 42a. The energization of coil 52 through thiscircuit opens valve 53, which permits gas to flow to 6 the main burner54 where it will be ignited by thepilot burner 11.

If the pilot burner goes out, the thermal probe 13 will contract inlength as it cools and will retract the switchoperating pin 27 to permitthe second switch contacts 37 and 41 to open and the first switchcontacts 36 and 38 to close. This will shut off the main burner 54 andwill energize the ignition coil 15 again to relight the pilot burner 11,after which the second switch contacts 37 and 41 will close again tore-open the main burner valve 53.

The present arrangement of the switch contacts, the terminals and theignition coil is advantageous in that it enables a single low voltagepower source to provide the power supply for the complete ignitionsystem.

Although this invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A burner ignition unit comprising a housing having a recess thereinand an opening leading into said recess,

an elongated pilot burner attached to said housing and projectingtherefrom,

an ignition coil positioned to ignite the pilot burner,

terminals attached to said housing and rigidly supporting said ignitioncoil and providing electrical connections thereto,

a support member attached to the end of said pilot burner away from saidhousing,

an adjusting screw threaded in said support member and having a recess,

a thermal probe supported at one end in said adjusting screw recess andextending therefrom toward said housing and having a free end slidablydisposed in said opening in the housing, said thermal probe beingpositioned to be heated by the pilot burner and having a thermalexpansion substantially greater than that of said pilot burner,

and a switch in said housing recess positioned to be operated by saidthermal probe as the latter expands longitudinally relative to saidpilot burner.

2. A burner ignition unit comprising a housing having a recess thereinand an opening leading into said recess, an elongated pilot burnerattached to said housing and pro ecting therefrom,

a support member attached to the end of said pilot burner away from saidhousing,

a thermal probe supported at one end by said support member andextending therefrom toward said housing and having a free end slidablydisposed in said opening in the housing, said thermal probe beingpositioned to be heated by the pilot burner and having a thermalexpansion substantially greater than that of said pilot burner,

a switch in said housing recess comprising an electrically conductiveflexible and resilient leaf spring having a movable free end, first andsecond movable contacts on the opposite faces of said leaf springadjacent its free end, first and second fixed contacts on opposite sidesof said leaf spring adjacent its free end for engagement respectively bysaid movable contacts, said leaf spring having an inherent bias towardsaid opening in the housing to position said first movable contactengaging said first fixed contact and to position said second movablecontact out of engagement with said second fixed contact,

separate terminals mounted on said housing and connected respectively tosaid leaf spring, said first fixed contact, and said second fixedcontact,

and a switch operator of electrical insulation material between the freeend of said thermal probe and said leaf spring to move the latteragainst its bias to disengage said first movable contact from said firstfixed contact and to position said second movable contact in engagementwith said second fixed contact in response to expansion of the thermalprobe by heat from the pilot burner and from the ambient tern perature.

3. A burner ignition unit comprising, a housing having 50 side thereofand 18 attached to one end of said ignition coil, a third terminalrigidly mounted on said opposite side of said housing and connected tosaid second fixed contact,

a fourth terminal rigidly mounted on said opposite side of said housing,said fourth terminal having a leg which extends from the housing alongthe pilot burner at the opposite side thereof and is attached to theopposite end of said ignition coil,

and a switch operator of electrical insulation material connected to thefree end of said thermal probe and engageable with said leaf spring tomove the latter against its bias to disengage said first movable conapair of opposite sides and a recess between said sides tact from saidfirst fixed contact and to move said and an opening in one of said sidesleading into said resecond movable contact into engagement with saidcess, second switch contact in response to lengthwise exan elongatedtubular pilot burner attached to said pansion of the thermal probe byheat from the pilot housing and extending away from said housing atburner. said one side thereof, said pilot burner presenting l5 *5. Aburner ignition unit comprising a housing having ignition and flame portmeans spaced from said an opening, h i an elongated pilot burnerattached to said housing and an ignition coil extending in ignitingrelation to the projecting therefrom,

il t b 21 support member attached to the end of said pilot an end plateattached to the end of said pilot burner 2t} burner y from Said housing,

away f id h i a thermal probe supported at one end by said support an lt d th l probe Supported t one d by member and extend-ing therefromtoward said houssaid end plate and extending therefrom toward said ingand having a tffie 6nd ly isposed in Said housing and having a free endslidably disposed in p g in the housing, Said thermal Probe hsihg saidopening in the housing, said thermal probe positioned to be heated bythe pilot burner and havbeing positioned to be heated by flame at saidfiame g a thermal expansion substantially greater than port means of thepilot burner and having a therthat Of Said Pilot burner, mal coefficientof expansion substantially greater 3 double throw Switch Said housingComprising 3 h h f id il b resilient leaf spring having a movable freeend coa switch in said housing recess comprising a cantilever- Operahlhalternatively with first and nd fiX d mounted, flexible and resilientleaf spring of elec- Contacts, trically conductive material having amovable free Said leaf Spring having an inherent s ward said end, firstand second movable contacts on the op- Opening in th@ housing toPosition Said leaf Spring posite faces of said leaf at its free end,first and g engaging Said first fixed Contact, second fi d contacts onopposite id of id l f and a switch operator of electrical insulationmaterial Spring at its fr e and i f ti mlationship between the free endof said thermal probe and said respectively to said first and secondmovable contacts teat Spring to move the latter against its bias to forengagement by the latter, said leaf spring havengage said leaf springfrom said first fixed contact ing a bias toward said opening in thehousing to 40 h to position Said leaf p g in ahgtlgemeht With i i id fit bl Contact engaging id said second fixed contact in response tolongitudinal first fixed contact and to position said second mov-Xpahsioh of the thermal Probe y twat m th able contact away fromengagement with said second Pilot burner and from the ambienttemPeratul'efixed contact, ;a first terminal rigidly mounted on theopposite side 45 References Cited b the Examiml of said housing andconnected to said leaf spring, UNITED STATES PA :a second terminalrigidly mounted on said opposite side of said housing and connected tosaid first fixed 2:13 1 2 contact, said second terminal having a legwhich ex- 3183959 5/1965 Romanelfi 158 128 X tends from the housingalong the pilot burner at one FREDERICK L. MATTESON, 111., PrimaryExaminer. E. G. FAVORS, Assistant Examiner.

1. A BURNER IGNITION UNIT COMPRISING A HOUSING HAVING A RECESS THEREINAND AN OPENING LEADING INTO SAID RECESS, AN ELONGATED PILOT BURNERATTACHED TO SAID HOUSING AND PROJECTING THEREFROM, AN IGNITION COILPOSITIONED TO IGNITE THE PILOT BURNER, TERMINALS ATTACHED TO SAIDHOUSING AND RIGIDLY SUPPORTING SAID IGNITION COIL AND PROVIDINGELECTRICAL CONNECTIONS THERETO, A SUPPORT MEMBER ATTACHED TO THE END OFSAID PILOT BURNER AWAY FROM SAID HOUSING, AN ADJUSTING SCREW THREADED INSAID SUPPORT MEMBER AND HAVING A RECESS,